An organic electroluminescence (EL) device has many attractive features as a display (multicolor light-emitting apparatus) such as low consumption power, small thickness, high-response speed, wide viewing angle or the like. As for an organic EL display using such an organic EL device, an all-deposition type display in which an emitting layer or the like are formed by depositing a low-molecular weight organic material has been put into practical use in a small-sized display such as a mobile phone.
In an all-deposition type organic EL display, materials are not used efficiently. In addition, a vacuum system or a color-coding mask for a deposition layer is required for production, and hence, film formation for a large-sized screen is difficult, whereby it has problems regarding a reduction in cost and an increase in size.
On the other hand, if a coating-type organic EL display in which an emitting layer or the like are formed by coating a high-molecular organic material by ink-jetting, nozzle printing, gravure printing or the like can be realized, there is a possibility that the problems associated with a deposition method as mentioned above can be solved (a display in FIG. 2, for example, HIL: hole-injecting layer, IL: interlayer (hole-transporting layer), LEP: high-molecular light-emitting polymer, ETL: electron-transporting layer). However, a coating-type organic EL display has an insufficient luminous efficiency and a shorter lifetime as compared with an all-deposition type display. In particular, it has a serious problem in blue emission.
Patent Document 1 discloses a hybrid-type organic EL display which is a combination of a coating-type display which is inexpensive and enables the screen size to be increased and a high-performance deposition type display (FIG. 3).
The organic EL display shown in FIG. 3 is an organic EL display obtained by a method in which a red-emitting layer and a green-emitting layer (LEP) are separately provided by a coating method, and a blue-emitting layer is allowed to be a common layer (Blue Common layer) by depositing a low-molecular material. The display shown in FIG. 3 can enhance the blue emission performance, and it is possible to reduce color-coding steps from 3 to 2 steps. However, since a coating type hole-transporting layer (IL) is in contact with the anode of the blue-emitting layer, emission performance of blue color was not sufficient.
The display shown in FIG. 4 which is disclosed in Non-Patent Document 1, Patent Document 2 or Patent Document 3 exhibits a significant improvement in blue emission performance due to the provision of a hybrid connecting layer (HCL) between the blue common layer as a deposition layer and a coating layer.
As the material of HCL, in order to improve the blue emission performance, not only matching between the hole-injecting and transporting properties and the blue-emitting layer, electron-injecting and transporting properties to a red-emitting layer and a green or yellow-emitting layer formed by coating are required; in particular, when a red-emitting layer and a green or yellow-emitting layer formed by coating are phosphorescent emitting layers, a higher triplet energy (T1) is also required in order to prevent diffusion of triplet energy. As the material for HCL, when a common hole-transporting material, a common electron-transporting material or a common high T1 material are independently used singly, there is a problem that comprehensive improvement in performance or color reproducibility, in particular, suppression of change in chromaticity by current of an organic EL multicolor light-emitting apparatus cannot be attained satisfactorily. That is, due to diffusion of triplet energy from the red, green or yellow-emitting layer when an organic EL multicolor light-emitting apparatus is driven (i.e. when driving current is changed), the blue common layer emits light, and as a result, blue emission is mixed with red, green or yellow emission, whereby color mixing occurs.